The proposed work for the coming year falls into three parts: 1) We shall use H3 labeled copy RNA as a probe for the intranuclear location of satellite DNA sequences by in situ hybridization and autoradiography. We will simultaneously prepare slides which will determine whether our previous identification of the nuclear location of Drosophila virilis satellites I, II, and III were correct, and also to explore the sequence relationship, if any, between the A-T rich satellites and the A-T rich DNA in some of the bands of the polytene chromosomes both in Drosophila virilis and Drosophila melanogaster; 2) We shall characterize the behavior of mouse satellite DNA containing chromatin in the mitotic cell cycle of cultured mouse L-cells, and possibly mouse white cells. It is hoped that this study will shed light on the bewildering array of configurations observed in various interphase cell types and meiotic cell states we have thus far observed. In this study we will depend on the fluorescent dye 33258 Hoechst to specifically localize mouse satellite DNA; 3) We shall continue our major effort to determine suitable conditions for the study of sequence specific nuclear DNA binding proteins, and to identify and isolate, if possible, proteins which bind specifically to mouse satellite DNA. BIBLIOGRAPHIC REFERENCES: John E. Mayfield and John R. Ellison, "The Fluorescence Localization of Mouse Satellite DNA in Interphase Nuclei", Chromosoma 54, 27-31 (1976). R. Marino, K.N. Saksena, M. Schuler, J.E. Mayfield, and P.A. Lemke, "Double-Stranded Ribonucleic Acid in Agaricus bisporous", Applied and Environmental Microbiology 31, (1976).